This invention relates to rotary position detectors for an internal combustion engine, which is capable of detecting a rotary position of an internal combustion engine for controlling the ignition timing.
FIG. 5 shows a conventional rotary position detector for an internal combustion engine such as shown in Japanese U.M. Patent Application Kokai No. 60-23714. This rotary position detector includes a cam timing pulley 1 attached to a cam shaft 2 with a bolt 3. A belt cover 4 covers the entire timing pulley 1. A rotary position sensor 6 is secured to an engine body. A pair of circular ribs 7' and 8' are formed integrally and concentrically with the timing pulley 1. The circular ribs 7' and 8' each have slits so that their passing through the sensor 6 permits the sensor 6 to ouput a signal corresponding to the rotary angle of the cam shaft 2.
To assemble the rotary position detector, the sensor 6 is secured to the engine body and, then, the timing pulley 1 with the circular ribs 7' and 8' is attached to the cam shaft 2. Consequently, the measuring accuracy of the rotary position detector depends upon the combined accuracy of all the associated components and is unable to determine before completion of the assembly. This makes it impossible to give warranty to performance of the rotary position detector itself. Where the timing pulley 1 is dismantled and assembled again due to a defect of another component, the accuracy of the detector can change, thus failing to provide a consistent performance. In addition, dust and dirt can adhere to the sensor of the detector, hindering accurate measurements of the rotary position. Moreover, the detector has been susceptible to electromagnetic noise.